This invention generally relates to print head cleaning apparatus and methods and more particularly relates to a cleaning apparatus and method of assembly therefor for cleaning an inkjet print head.
An ink jet printer produces images on a recording medium by ejecting ink droplets onto the recording medium in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the ability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
More specifically, an ink jet printer comprises a print head cartridge that includes a plurality of ink ejection chambers and a plurality of ink ejection orifices in communication with respective ones of the ink ejection chambers. At every orifice an ink ejector is used to produce an ink droplet. In this regard, either one of two types of ink ejectors may be used. These two types of ink ejectors are heat actuated ink ejectors and piezoelectric actuated ink ejectors. With respect to piezoelectric actuated ink ejectors, a piezoelectric material is used. The piezoelectric material possesses piezoelectric properties such that an electric field is produced when a mechanical stress is applied. The converse also holds true; that is, an applied electric field will produce a mechanical stress in the material. When a piezoelectric actuated ink ejector is used for inkjet printing, an electric pulse is applied to the piezoelectric material causing the piezoelectric material to bend, thereby squeezing an ink droplet from an ink body in contact with the piezoelectric material. The ink droplet thereafter travels through the ink ejection orifice and lands on the recording medium. One such piezoelectric inkjet printer is disclosed by U.S. Pat. No. 3,946,398 titled xe2x80x9cMethod And Apparatus For Recording With Writing Fluids And Drop Projection Means Thereforxe2x80x9d issued Mar. 23, 1976 in the name of Edmond L. Kyser, et al.
With respect to heat actuated ink ejectors, such as found in thermal ink jet printers, a heater locally heats the ink body and a quantity of the ink phase changes into a gaseous steam bubble. The steam bubble raises the internal ink pressure sufficiently for an ink droplet to be expelled through the ink ejection orifice and toward the recording medium. Thermal inkjet printers are well-known and are discussed, for example, in U.S. Pat. No. 4,500,895 to Buck, et al.; U.S. Pat. No. 4,794,409 to Cowger, et al.; U.S. Pat. No. 4,771,295 to Baker, et al.; U.S. Pat. No. 5,278,584 to Keefe, et al.; and the Hewlett-Packard Journal, Vol.39, No. 4 (Aug. 1988), the disclosures of which are all hereby incorporated by reference.
The print head cartridge itself may be a carriage mounted print head cartridge that reciprocates transversely with respect to the recording medium (i.e., across the width of the recording medium) as a controller connected to the print head cartridge selectively fires individual ones of the ink ejection chambers. Each time the print head traverses the recording medium, a swath of information is printed on the recording medium. After printing the swath of information, the printer advances the recording medium the width of the swath and the print head cartridge prints another swath of information in the manner mentioned immediately hereinabove. This process is repeated until the desired image is printed on the recording medium. Alternatively, the print head cartridge may be a page-width print head cartridge that is stationary and that has a length sufficient to print across the width of the recording medium. In this case, the recording medium is moved continually and normal to the stationary print head cartridge during the printing process.
Inks useable with piezoelectric and thermal ink jet printers, whether those printers have carriage-mounted or page-width print head cartridges, are specially formulated to provide suitable images on the recording medium. Such inks typically include a colorant, such as a pigment or dye, and an aqueous liquid, such as water, and/or a low vapor pressure solvent. More specifically, the ink is a liquid composition comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives and other components. Moreover, the solvent or carrier liquid may be water alone or water mixed with water miscible solvents such as polyhydric alcohols, or organic materials such as polyhydric alcohols. Various liquid ink compositions are disclosed, for example, by U.S. Pat. No. 4,381,946 titled xe2x80x9cInk Composition For Ink-Jet Recordingxe2x80x9d issued May 3, 1983 in the name of Masafumi Uehara, et al.
Such inks for inkjet printers, whether of the piezoelectric or thermal type, have a number of special characteristics. For example, the ink should incorporate a nondrying characteristic, so that drying of the ink in the ink ejection chambers is hindered or slowed to such a state that by occasional spitting of ink droplets, the ejection chambers and corresponding orifices are kept open and free of dried ink. However, it has been observed that ink can builds-up on the print head and electrical interconnect of the print head. This ink build-up can result from the following three main sources: (1) ink puddling and splatter as ink is ejected; (2) ink aerosol condensation on the print head; and (3) ink redeposited by a service station cap and wiper. Such ink build-up may lead to the following undesirable results: (1) wet ink shorting the electrical interconnect of the print head thereby causing electrical malfunction of the print head; (2) paper fiber tracks causing unwanted lines of ink on the recording medium due to dragging of wet paper fibers stuck to the ink on the print head; (3) poor ink ejection orifice performance causing drop ejection errors, and drop velocity or drop volume degradation; and (4) ink drops falling-off the print head causing unwanted ink spots on the recording medium.
In addition, the inkjet print head cartridge is exposed to the environment where the inkjet printing occurs. That is, the previously mentioned ink ejection orifices are exposed to many kinds of air born particulates, such as dust, dirt and the previously mentioned paper fibers. Particulate debris may accumulate on surfaces formed around the orifices and may accumulate in the orifices and chambers themselves. That is, the ink may combine with such particulate debris to form an interference burr that blocks the orifice or that alters surface wetting to inhibit proper formation of the ink droplet. Blocking the orifice interferes with proper ejection of ink droplets, thereby altering the flight path of the ink droplets and causing the ink droplets to strike the recording medium in unintended locations. The particulate debris and ink build-up should be cleaned from the print head surface and orifice to restore proper droplet formation and proper ink droplet trajectory.
For all the foregoing reasons, it is important to clean the print head of unwanted ink and debris. In some prior art devices, this cleaning is accomplished by wiping the print head or by absorbing ink and debris from the print head.
A representative inkjet print head cartridge cleaner using a wiper blade to wipe the print head is disclosed by U.S. Pat. No. 5,907,335 titled xe2x80x9cWet Wiping Printhead Cleaning System Using A Non-Contact Technique For Applying A Printhead Treatment Fluidxe2x80x9d issued May 25, 1999 in the name of Eric Joseph Johnson, et al. and assigned to the assignee of the present invention. The Johnson, et al. patent discloses cleaning in printers employing a xe2x80x9cwiperxe2x80x9d blade, which slidingly engages and wipes a nozzle orifice plate surface of a print head cartridge to remove excess ink and accumulated debris. Removal of excess ink and accumulated debris is intended to improve print head performance and print quality. According to the Johnson, et al. disclosure, the cleaning system comprises a print head service station including a source of treatment fluid located near a cap belonging to the service station. The cap is brought into sealing contact with the print head. A wiper, which is included in one embodiment of the service station, comes into contact with the print head for removing dried ink and debris. The treatment fluid lubricates the wiper to reduce wear of the wiper. Also, the treatment fluid dissolves some of the dried ink residue accumulated on the print head. In addition, the treatment fluid leaves a thin film, which does not readily dry, so that ink residue and other debris subsequently deposited on the print head over the layer of the fluid are more easily wiped-off. Scrappers are provided within the service station to clean the wipers.
Another technique for cleaning an inkjet print head is disclosed in Japanese Patent JP 3-189163 titled xe2x80x9cInk Jet Recorderxe2x80x9d issued Aug. 19, 1989 to Canon, Incorporated. The Canon patent discloses a method of removal of paper powder, dust, ink or the like from the front discharge portion of a print head. More specifically, when the print head is positioned at a cleaning location in the printer by means of a carriage motor, the print head is pushed into contact with a ribbon of porous material. Ink, bubbles, e.t.c. are absorbed from the discharge portion of the print head by capillary action between the discharge portion and the porous material. The amounts of ink, bubbles, e.t.c., that may contain paper powder or dust, are absorbed in proportion to contact time with the porous material. After cleaning, the print head is then returned to a printing position by operation of the carriage motor. After confirming that the print head is no longer at the cleaning location, the porous material is advanced to ready another portion of the porous material for the next cleaning event.
Although prior art print head cartridge cleaning techniques, such as disclosed by the Johnson, et al. patent, may function satisfactorily, it has been observed that ink will build-up on the wiper over time. This results in diminished effectiveness of the wiper over the life of the wiper. Although scrapers, such as disclosed by the Johnson et al. patent, are sometimes provided to clean the wiper, use of scrappers do not eliminate the root cause of the problem and can themselves experience ink build-up that diminishes scraper effectiveness over time. Moreover, although the Canon patent discloses a porous material for removal of ink, bubbles, e.t.c. that may contain paper powder or dust, there is apparently no disclosure in the Canon patent that the porous material remains wrinkle-free in order to enhance cleaning effectiveness when the porous material is brought into contact with the print head. Also, according to the Canon patent, the porous material must remain in contact with the print head for a specified time to satisfactorily absorb ink, bubbles, paper powder or dust by the relatively slow process of capillary action. Use of the Canon cleaning technique therefore increases cleaning time.
Therefore, what is needed is a cleaning apparatus and method of assembly therefor for cleaning an inkjet print head, which apparatus and method (1) eliminate need for wipers and scrapers, yet removes ink build-up and particulate debris from the exterior surface of the print head to avoid wet ink shorting the electrical interconnect of the print head; (2) remove paper fiber tracks causing unwanted lines of ink on the recording medium; (3) improve poor ink ejection orifice performance that otherwise cause drop ejection errors, drop velocity or drop volume degradation; (4) reduce risk of ink drops falling-off the print head causing unwanted ink spots on the recording medium; and (5) avoid reliance on the relatively slow process of capillary action to clean the print head.
In a broad form, the invention is a cleaning apparatus and method of assembly therefore for cleaning an inkjet print head. The cleaning apparatus comprises a web supply for supplying a web therefrom. A web receiver is associated with the web supply for receiving the web, the web being capable of extending from the web supply to the web receiver and slidably engaging the print head for cleaning the print head. A web drive is associated with the web supply and the web receiver for driving the web from the web supply to the web receiver. The web drive is adapted to pull the web from the web supply with a first tension force and to pull the web onto the web receiver with a second tension force greater than the first tension force, so that the web is wrinkle-free while the web slidably engages the print head.
According to an aspect of the present invention, the cleaning apparatus comprises a web supply wound about a freely rotatable first spindle. Disposed proximate the first spindle is a web receiver comprising a rotatable second spindle for receiving the web thereon. In this manner, the web extends from the first spindle to the second spindle while the web slidably engages the exterior surface of the print head for cleaning the surface of the print head.
The cleaning apparatus further comprises a web drive coupled to the second spindle for driving the web from the freely rotatable first spindle to the second spindle. In this regard, the web drive comprises a drive roller concentrically mounted on a third spindle disposed proximate the first spindle. A portion of the web extending from the first spindle wraps partially around the drive roller, so that the web is pulled from the first spindle as the drive roller rotates. The web drive is also coupled to the second spindle. That is, the web drive simultaneously pulls the web onto the second spindle as the drive roller, which belongs to the web drive, pulls the web from the first spindle. In other words, the web drive both pulls the web from the web supply and pulls the web onto the web receiver. Moreover, it is the portion of the web that is wrapped partially around the drive roller that engages the print head surface for cleaning the print head surface.
The web drive further comprises a gear train for controllably rotating the second spindle (web receiver) and the third spindle (drive roller). Coupled to the second spindle is an adjustable overdrive slip clutch. The overdrive slip clutch is adjustable for applying a predetermined amount of sliding friction to the second spindle to control speed of rotation of the second spindle. Controlling speed of rotation of the second spindle will control the forward tension acting on the web. In this regard, the overdrive slip clutch can be adjusted to apply a desired forward tension force acting on the web. Moreover, the portion of the web that partially wraps around the drive roller effectively functions as a xe2x80x9cpassive slip clutchxe2x80x9d arrangement. The passive slip clutch arrangement applies a predetermined amount of friction between the drive roller and the web, depending on a predetermined xe2x80x9cwrap anglexe2x80x9d (i.e., angle formed by the web as it wraps partially around the drive roller), so that the drive roller moves the web without slippage. In this regard, the passive slip clutch arrangement applies a desired back tension force acting on the web. Adjustment of the overdrive slip clutch and presence of the passive slip clutch allows the overdrive slip clutch and the passive slip clutch to cooperatively act to hold the web in tension, so that the web remains wrinkle-free. It is important that the web remains wrinkle-free. This is important to ensure that the surface of the web will contact the surface of the print head without gaps in contact coverage. This enhances cleaning effectiveness compared to a web having wrinkles.
An actuator is also provided for actuating the gear train. Actuating the gear train in turn rotates the second spindle and the drive roller a predetermined amount. In this regard, after the print head is sufficiently cleaned by the web, the actuator indexes the web by rotating the second spindle and the drive roller the predetermined amount in order to present an unused portion of the web for the next cleaning event.
The cleaning apparatus further includes a plurality of conventional spittoons for receiving ink ejected or xe2x80x9cspitxe2x80x9d from the cartridge orifices to clear the orifices of dried ink and debris. The cleaning apparatus also includes a plurality of conventional capping stations for capping the orifices when the print head is not in use, so that risk of ink dry-out is reduced. Thus, the cleaning apparatus may inventively include traditional spittoons and/or capping stations in combination with the web and web drive for enhanced cleaning effectiveness.
A feature of the present invention is the provision of a web capable of slidably engaging the print head for cleaning the print head.
Another feature of the present invention is the provision of a web drive to precisely drive the web, so that the web is wrinkle-free while the web slidably engages the print head.
An advantage of the present invention is that use thereof eliminates need for wipers and scrapers, yet removes ink build-up and particulate debris from the exterior surface of the print head.
Another advantage of the present invention is that use thereof (1) avoids wet ink shorting the electrical interconnect in the print head; (2) removes paper fiber tracks causing unwanted lines of ink on the recording medium; (3) improves poor ink ejection orifice performance that otherwise cause drop ejection errors, drop velocity or drop volume degradation; and (4) reduces risk of ink drops falling-off the print head causing unwanted ink spots on the recording medium.
Yet another advantage of the present invention is that use thereof reduces cleaning time.